(1) Field of the Invention
This invention relates to polymeric electrodes. More particularly, this invention relates to electrodes for non-aqueous secondary batteries composed of predoped conjugated backbone polymers.
(2) Prior Art
Conjugated backbone polymers, e.g., polyacetylene, polyphenylene, polyacenes, polythiophene, poly(phenylene vinylene), polyazulene, poly(phenylene sulfide), poly(phenylene oxide), polythianthrene, poly(phenylquinoline), polyaniline, poly(thienylene vinylene), poly(furylene vinylene), and polypyrrole, and their derivates have been suggested for use in a variety of applications based upon their characteristic of becoming conductive when oxidized or reduced either chemically or electrochemically. The secondary battery application described by, e.g., MacDiarmid et al. in U.S. Pat. No. 4,321,114 (1981); J. de Physique, Colloque C3, Vol. 44 (1983), articles beginning on page 579, page 615 and page 537; and K. Kaneto et al., Japanese J. of Applied Physics, Vol. 22, pp. L567-L568 (September 1983) and pp. L412-L414 (July 1983), employs one or more electrodes having conjugated backbone polymers as the electroactive material. Such electrodes can, for example, be reversibly complexed with alkali metal or tetraalkylammonium cations during battery cycling, most commonly with insertion of cations into a polymer anode (the negative battery electrode) occurring during charging. The more such cations are inserted, the more conductive the electrode becomes and the more cathodic the potential of the anode becomes.
U.S. Pat. No. 4,002,492 discloses electrochemical cells having an anode consisting essentially of lithium aluminum alloys that contain lithium in amounts between about 63% and 92% and the balance essentially aluminum. Anodes composed of lithium and aluminum are also disclosed in Rao, et al., J. Electrochem. Soc. 124, 1490 (1977), and Besenhard, J. Electroanal. Chem., 94, 77 (1978).
European Patent No. 0070107 Al; Murphy et al., J. Electrochem. Soc., 126, 349 (1979) and Murphy et al., Mat. Res. Bull., 13, 1395 (1978) disclose batteries based on lithium intercalation in layered dichalcogenides.
Composite structures of a conjugated backbone polymer and a non-electroactive material have been described in U.S. Pat. No. 4,294,304 and in the above J. de Physique issue, articles beginning on page 137 and on page 151. Representative other components that have been blended with polyacetylene or onto which polyacetylene or polypyrrole have been deposited include polyethylene, polystyrene, graphite, carbon black, NESA glass and silicon. In selected instances, such composite structures have been suggested for use in batteries, see Showa Denko K. K., European Published Patent Application 76,119 (1982).
U.S. Pat. No. 4,668,596 is directed an anode and to batteries containing the anode. The anode comprises a mixture of a conjugated backbone polymer and another electroactive material selected from the group consisting of metals which alloy with alkali metals such as aluminum and lead and alkali metal cation insertions materials such as transition metal chalcogenides.
Conventional batteries have heretofore been constructed in which a conjugated backbone polymer is one of the electroactive materials, such batteries suffer from a number of disadvantages. For example, impurities, including oligomers, often exist in the polymer. These form species which are soluble in the electrolyte solvent and which may adversely affect battery performance. These adverse effects include capacity loss and cell self-discharge. Moreover, the large volume changes of the polymer before and after doping may seriously affect electrode shape and uniformity and may induce cell shorting during cycling.